The pressing need for clean and renewable energy sources has inspired significant research focused on the improvement of photovoltaics, batteries, and catalysts [1]. Due to their inherently large surface area and manufacturability, nanomaterials have received specific attention for these alternative energy applications [2-4]. For example, the photoactive electrode in dye sensitized solar cells (DSSC) employs titanium dioxide nanoparticles, leading to 10% device efficiency with relatively simple processing [5]. Further improvements have been realized by combining multiple nanomaterials in nanocomposite films. In particular, because of their high electrical conductivity, excellent chemical and mechanical stability, and large surface area, carbon nanotubes show promise as electrodes and catalyst supports [6-23]. The combination of carbon nanotubes and platinum nanoparticles has been especially successful for fuel cell applications, where multifold efficiency improvements have already been demonstrated [24].
Many strategies for decorating carbon nanotubes with platinum nanoparticles have been previously developed. Solution and supercritical liquid functionalization [14] schemes have the advantage of exploiting the entire carbon nanotube surface, although it is necessary to maintain well dispersed carbon nanotubes during the platinum nanoparticle attachment and growth in order to obtain complete surface coverage. For example, covalent attachment of platinum has been achieved by chemical functionalization of the carbon nanotube surface [12]. In this approach, metal precursors covalently bind to carbon nanotube defects and are then chemically reduced to form platinum nanoparticles [6, 22, 25]. In addition, solution-based, noncovalent deposition procedures have been developed where perturbation of the carbon nanotube surface is minimized because the platinum is grown on a polymer that noncovalently encapsulates the nanotube [26, 27]. Surface deposition methods such as electrodeposition [11, 28, 29], evaporation [30], and pyrolysis [23], have also been employed to form platinum nanoparticles on carbon nanotube thin films. In select cases, these surface methods have also yielded platinum deposition selectively at carbon nanotube defect sites [31, 32]. While surface deposition schemes possess some processing advantages compared to solution-phase techniques; however, they typically result in only the top surface of the carbon nanotube film being decorated with platinum nanoparticles.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.